Switchboard-circuit and signaling apparatus



(NQ Model.)

P. W. DUNBARJ 8u E, S. 0.]MAY. SWITGHBOARD CIRCUIT AND SIGNALING APPARATUS.

N'Aogel 4PmernedNov.2:3;1893.

UNITED STATES PATENT OFFICE.

FRANCIS WV. DUNBAR AND EDMUND C. MAY, OF NEWARK, JERSEY, ASSIGN ORS TO THE AMERICAN TELEPHONE AND TELEGRAPH COMPANY,

VOF NEW YORK. l

swlTcHBoARD-CIRCUIT AND SIGNALING APPARATLJs,,.l

SIECIFICATION forming part of Letters Patent No.1509,1367, dated November 2,8-, 1893..

Applicationiled March '7, 1892. Serial No. 424,080.' (No model.) I Y To all whom 'it may concern,.-

- Be it known that we, FRANCIS W. DUNBAR and EDMUND S. C. MAY, both residing at Newark, in the county of Essex and State ot New Jersey, have invented certain Improvements in Switchboard-Circuits and Signaling Apparatus, of which the following is aspecication.

This invention concerns multiple switchboards; and brieliy stated, its object is to provide a switchboard for the central ofce of a telephone exchange in which each substation s circuit shall be represented at the several sec- Y dicating annunciator located at some one of the switchboard sections, it being a matter of common practice to divide the annunciators of the several circuits among the several sections so that the callsof a given number of circuits are answered at each section. But as all lines have plug socket terminals at all sections, the circuit whose call is answerable at but one section, may be united to another circuit with which communication is desired, at the same section where the call was received, without regard to the location of the call annunciator of such called circuit. l

It has been customary to so arrange the circuits in multiple switchboards that the several circuit conductors in passing through the several sections were led successively through separable springjack contacts disposed in series in the circuit; and when so arranged it is obvious that the insertion of a plug connector into any springjack would not only bring about the connection of the conductor attached to said plug to the line represented by the contact spring of the jack in question, but would also (inasmuch as it would lift the said spring from its normal contact) break the original circuit through the switchployment ot' such a multitude of springjacks as were required, and also with the purpose of dispensing with the necessity ot" having a large number of variable contacts in series in the circuit (each of which experience has demonstrated providesthe nucleus fora possible fault) it has become desirable to'dispense with the serially arranged springjacks, and to adopt the normally discontinuous branch terminalsin the plug sockets, to which 6o reference was made in the initial paragraph of this specification.

It is obvious when switchboards are constructed upon the branch terminal plan, that some special construction must be adopted to been devised, our invention not being broadly new in this respect. For the purpose of providing that the call annunciator employed shall not act as a short circuiter yfrom one 8o side of the circuit to another, during the transmission of voice currents, which have a high rate of change, we adopt the well known expedient of constructing it in such away that it shall have a high coefticient of self induction; as is likewise done with the helices of the clearing out or disconnecting annunciator, which also during through communication is bridged between the direct and return circuits of the main telephone circuit. 9o But to achieve theobject of 'our invention we provide the callannunciator with two helices, one of which is in the main circuit and made active by the circulation of the calling currents; whilethe other isin anormallyincomplete electric circuit, which is completed by the act of insertinga plug connector into any plug socket of the circuit to which the particular annunciator belongs, and which thereupon energizesthe magnetizablecore of the roo extra helix, setting up a steady magnetization therein, and enabling the said core thereupon to hold the drop shutter in place, preventing it from being responsive to any call currents which may come in, or which are sent out as long as the circuit remains closed; which of course is as long as the plug remains in the socket. This is brought about by uniting one of the terminals of the extra helix with one pole of the battery or other generator, and by extending a conductor from its other terminal to all of the plug sockets of the circuit to which the annunciatorbelongs, branching it t a-connection with the, several metal framepieces of each. The connecting plugs each have f three conducting surfaces insulated from each other, two of which correspond with the two main circuit branch terminals, while the third is adaptedy to make contact with the socket frame piece. This third contact surfaceof the plug is in permanent union through a suitable conductory with the second pole of the generator in whose circuit is the auxiliary helix of the'annunci-ator, and thus it is, that upon the insert-i011 Of the plug a current circulates in such helixand the annunciator drop is prevented from responding to calling or clearing out currents. The shutter or its controlling armature lever is made of iron, and either may be organized to forrn'the armature of thesaid auxiliary helix and to be held there.- by. This extra conductor uniting the frames of theseveral plug sockets of each main circuit, may andpreferably will serve as a portion ofthe busy test circuit, and at any section of the switchboard, an operator may determinewhether a given line is busy atsome other section byvtouohing the tip of the plug connector to the frame piece of the socket of theA linedesired, which operation brings the telephone. of the'said operator into a derived circuit of the shutter retaining battery, and produces a well defined sound in said telephonegprovided-the tested line be busy; while, should said line be at liberty, there is no retaining battery connected with any of its sock-et frames and no such sound will be produced, so that the testing operator will know that the line is not busy. Y

The invention therefore comprises the provision for each circuit of amultiple switchboard,of anelectromagnetic retaining device for. the call annunc'iator which is brought into action through the act of inserting the connecting plug, and which causes attraction to be direct-ly exercisedy upon the annunciator shutter or its controlling lever as long as the connecting plug remains so inserted.

In the drawings Figure l is a conventional diagram of the central office end of two telephone circuits, illustrative of their connectionsin a branch terminal multiple switchboard, and their annunciator retaining circuits. Figs. 2 and 3 are skeleton forms of two styles of ,annnunciator either of which may be employed.

Two main circuits l and 2, are shown as frames of the same circuit. Thus each cir.

cuit has three wires through the switchboard. At some one switchboard section, each circuit is provided with a call annunciator a, having two distinct and independent electromagnetic helices a and. a2; with the first of` which af only, however we are at present concerned. One of the ends of the helix a is united to the circuit wire Z, and the other tothe circuit wire Z? so that the helix a is directly included in the said circuit. The plug socket con. nections 3V and It being branch terminals,the insertion of a plug connector does not disconnect the annunciator helix a which consequently bridges the circuit. when a connec-tion is made with a second circuit, but the said helix having a high apparent resistance, by reason of it being constructed to present arelatively high self ind-uction,does not practically cause'a loss of working current.

Figs. 2 and 3 exhibit alternative forms of construction which may be adoptedl for 4the annunciator a; the helices howeverv not being shown. InFig, 2, m is the central iron core, and m the tubular iron casing thereof, having an end piece q. On thisr core.4 and within the tube is Wound the helix a for connection with the main line circuit. The armature r is fulcrumed at e, and has secured at a. right angle an armature lever h, which by a retaining hook 7a2-at its end, ordinarily engages a signal shutter or drop s, keeping the same from falling and giving thesignal; but is capable otdisengaging itself therefrom and permitting the same to befreed from its control, when the armature r is attracted by the core m, made magnetic by the circulation round it'of callingcurrents. Mechanically securedto the inner end of the core m,but magnetically insulated therefrom by the plate of brass or like material andthe brass screw fu, is a second and preferably shorter iron core m2 formed by theA cheek pieces y, y2 which are made of any suitable material into a spool for the reception of the local helix c2.- The signal shutter s is made of iron, and is thus susceptible to magnetic attraction. It is evident that if a steady current becausedto circulate in the helix a? roundthecorem?, sufflciently strong to practically magnetize the same,l the iron shutters will be attracted y fore when acurrent is maintained Ythrough helix a2, calling currents sent through the helix a will not be'able to responsively actuate the annunciator.

The annunciator shown in Fig. 3, is of -a slightly diiferent type. In manyrespects the construction'is similar, but the shutter s is not, or need not be, magnetic; the shorter or supplementary iron core, is provided at each end with an iron pole piece m3; and the ar mature lever h in this case is of iron, so that it is attracted and prevented from liberating the shutter when the current Hows .in the auxiliary helix a2.

Referring once more to Fig. l, the wire 7 connecting in each circuit its several plug socket frames fyextends to one end of the auxiliary helix a2 of the annunciator a of 1 such circuit, the other end of said helix being conductor liexible cord, havihg plug terminalv connectors P. The plug sockets D and D2 which are united by these plugs are su pposed -of course to be located at the same switchboard section M. The plugs P correspond with the plug sockets D in that they each have upon their stem three conducting surfaces, e., the tip p4 to make contact with the branch terminal 3; a front sleeve surface p3 adapted to contact with the branchterminal 4; and a rear sleeve su rface 192, arranged to tit in the socket frame f and to make electrical contact therewith; and the said three conducting surfaces are insulated from each other'by non-conducting rings i i. The three conductors which extend between each pair of plugs P, are in practice inclosed in a single exible cord. One of them 9 unites the tip contacts p4 of the said plugs; a second unites their front sleeve contacts p3, while the third 6, unites their rear sleeve contact p2, thereby bringingv the socket frame wires 7 of any two connected lines also into connection. To any point on the conductor 6, is joined a wire 5 leading from a generator b, such as a battery of necessarystrength, and the other pole of said generator is connected to earth or to anomnibus return to which the several earth wires of the helices a2 would in that case also be united. Since the conductor 6 is thus connected as described with the said generator b, it follows irst that when the plug, or plugs, which terminate the said conductor are inserted into line sockets, as shown, and their conducting surfaces p2 are thus caused to make contact with the socket frame, the current of said generator will split at the point substantially equal parts 'Iiowing each way over the conductors 7 through the auxiliary helices a2 of the annunciators a and to' earth or return conductor. The cores m2 of such auxiliary helices are both thereby vitalized, and 'the signal shutters s are forcibly held up and prevented fromr falling (regardless of their engagement Y509,367*l p s by, or disengagement from thearma'ture lever h) by magnetic attraction exerted either directly upon the shutter itself or upon the vcontrolling leverthereof, as hereinbefore de.

scribed; and second, that under the same con-J ditions, all of the socket frames f of' the line or lines concerned, have their potential al-V tered by the electro `motive force of vsaid generator b and are brought into a state of charge; so that when a circuitis completed from any of the said socket frames, asignal maybe received upon any ,suitablev device arranged within such completed circuit; and this fact may be utilized as a busy test. I v i The first of the above recited facts is made available as followsz-A clearing ont or disconnecting annunciator e is-loopedacross bep tween each pair of connecting conductors 9 andlO by wires 14 and 15. Thisas well as thehelix a of the call annunciator areboth during a conversation connection between two lines included in derived circuits of 'the said two lines, but by being arranged to have amaximum self-induction, their apparent resistance is so high as presented vto the high rate'ot' change of voice currents, that there is no material loss due to their presence.

At the conclusion of a conversation itis desirable that a ring loff signal shall be sent from the substation, and thatthe clearing out annunciator shall be responsive, but thatt-he call annunciator shall be perfectly irresponsive thereto. The callsignals having relativelyT a low rate of change do in fact operate the clearing out drop eand give the disconnecting signal; but the line drop a, whether at the same or another switchboardsection, does not respond, because the magnetization of the auxiliary helix a2 by the steady current of the generator prevents the fall of the shu tter s.

The second of the above facts is made available as follows: Eachl switchboard section has an operators telephone t, usually as shown fitted for headwear. For certain purposes not germane to this invention, it is provided with two helices which are connected for the sake of a perfect balance between the two halves o and 02 of the secondary helix of a transmitter induction coil. To a point central between the said two helices, or if the telephone t has but one, from a point at the center thereof, an earth wire 1l is connected. The telephone loop is also, as in the case of the clearing Aout annunciator, bridged IOO across the two main conductors 9 and y10 of Y the said socket frame is charged as before explained, and a current will flow therefrom by way of the plug tip p4,.conductor 9, telephone branch wire 13 or 14 according to which plug is used, induction coil helix o2 and 0, and one half of telephone helix, to earth wire 11, and earth or return; causing. the telephone to emit a characteristic sound which is heard by the operator and which indicates the busy condition of the line.. But if the line be at liberty, vthe touched socket frame not being connected with the battery b isnot ro charged, no` such current will flow, and no sound will be heard in. the telephone, and the operator knowing therefore that the line is not busy,y at once inserts thel plugan.dl perfects the connection. One generator b may 15 of course be used for a number of connection cords; this being aI matter largely dey pendent upon theinternal resistance of the generatorv which in storage cells for example is very low. The common. return wire to zo which reference has been made isf indicated by the broken; lines 21. 5

Although for the sake of facility of. i-llu'stration metallic circuit lines only are show-n', it ist equally applicable to a mixed: system of z 5 metallicand' earth completed lines; thel test circuit being purely local and enti'relyinsullated fromy the main circuits.

Inzpracticeof coursev the connections of the operattrstel'ephone and clearingoutannungo ciator bridge loops are bothA controlled by suitable cam switches, there` being. one vannun'ia'tor foreach pairof cords-and but one teleph'onefor` annmber of such cords; but We have'not thought i-t necessary to show such 3 5 appliances and connections-since they are not necessary to a-full understanding ofl the in-ventionvandi itis sufficient to say that during the progress of af connection theannunzciator bridge is invariablyV connected, while 4o the telephoneis connectedonly during supervision.

Having now fully described our invention, we claim- 1. The combination with each main circuit of a call'annunciator having two helices, one included permanent-ly in themain circuit, and adapted,.when energized, to givethesignal, and the other includedwith aIsource of electricity in afnormally discontinuous local 5o circuit arranged to be completed by the'act of inserting a plug connector in any plug socket of said main line an'dto remain closed so longV as such plug occupies its socket, said second helix acting during such time to oph 5 5 pose and neutralize the action of the irst helix andprevent the signal from being given; substantially' as described.

2; In a switchboard apparatus, the combinationof a main circuit branching from its 6o conductors-to terminal contacts in each of a series of plug sockets; ann auxiliary conductor uniting the several conducting frames of the plug sockets of said main circuits; plug connectors at each switchboard section, eachv provided with contact terminalsarrangedto Iconnect with the main line socket terminals, and auxiliary or socket-framev terminals of any plug socket when inserted therein; conductors attached to said plug, one for each of the contact terminals thereof; an electrical generator united by one of its poles with that one of said conductors which upon the insertion ofv theplug connects with the socket frame, thfe remaining pole thereof being connected'to earth, or to the said auxiliary frame-uniting switchboard conductor; and a compound call annunci-ator having ahelix in the main circuit provided with a magnetiz- V able core, and an arma-ture adapted tobe attracted thereby, andA to display the call signal, and an auxiliary helix in circuit Withthe auxiliary frame-uniting conductor, provided also Witha coreada-pted to actin opposition to that of themain hel-ix, and towithhold the signal; whereby the insertion'of thesaidplug in any socket is enabled toattachl a connection to the main circuit. in parallel with the main annunciator heli-x, and` t'osimultaneously close the local battery circuit through i theauxi-liary aniiufnciator helix, su-bstantially as described.A

3. The combination i-n a multiple switchboard apparatus, of a compound callv annunciator having twoindependent electromagnetic helicesl each` with its own: coreone of which w-h-enenergized tends to release a1 dropand give asignal the other When energized tending toA maintain the drop in placev and toiwithh'oldl thesignal; a main line circuit extending to branch terminalcontacts in plug-sockets one at each switchboard sectio u, and permanently closed throughthe main or signal actuating annunciator helix; a normally open or discontinuous auxiliary circuit associated With each main circuitincluding the auxiliary or signal preventing helix; and a plug connector adapted for insertion into the main circuit plug sockets, and havin g contact surfaces registering; with the corresponding surfaces of said sockets; the said contact surfaces respectively beingterminals of'link conductors adapted to connect with the main circuit branch terminals, and of acompleting conductor leading from anlelectrical generator and arranged to close the said auxiliary cir cuit and to energize the said auxiliary helix as long as the plug remains insertedthe said plug being attached to the said: conductors, substantially asdescribed.

4. The combination of a closed circuit; a normally discontinuousw circuit, both being connected with the same plug sockets; an annunciator having an electromagnet permanently included in said closed circuit, and an armature therefor, which when attracted disengages a signal-shutter permitting the same to fall and give the signal, and having also an auxiliary electro magnetincludedin said normally discontinuous'circuit, the said magnet yhavin'gfor itsI armature the signal shutter or the disengaging'lever thereof,andactingwhen energized to attract the same, and to prevent the signal' frombeing given; a battery, or equivalent source of steady current; and a ICO IIO

plug connector adapted for insertion in the said plug sockets, forming when inserted therein a circuit changer for the closed circuit, anda circuit closer for the said normaiiy discontinuous circuit, closing the same through the said battery, and thereby exciting the said auxiliary eleetromagnet.

In testimony whereof We have signed our names to this specication, in the presence of two subscribing Witnesses, this 3d day of 1o March, 1892.

FRANCIS W. DUN BAR. EDMUND S. C. MAY. WVitnesses:

F. DE LYSLE SMITH, EDWARD W; BELL. 

